This invention relates to rotationally cast molded plastic articles having access openings for the connection of fittings thereto. More particularly this invention relates to non-metallic thermoplastic pump casings having reinforced flange connections and, according to another aspect of this invention, relates to rotationally cast filament-wound tank liners having reinforced access openings.
Presently, non-metallic pumps are made of engineered thermoplastics and are usually molded by an injection molding process. Since the tooling and mold costs for the injection molding of a pump casing are proportional to the size of the pump, injection molding has been used to produce relatively small fractional horsepower pumps. Prohibitive costs are involved in the production of large size pump casings adapted to withstand the hydraulic pressure and the volume of liquid being pumped.
Nevertheless, it is desirable to employ thermoplastic materials in the manufacture of pumps utilized as a horizontal closed coupled pump for swimming pools, waterfalls, K01 ponds, or as liquid transfer pumps. The advantages of using thermoplastic materials in the manufacture of thermoplastic pumps are their chemical resistance to withstand corrosion, toughness, light weight, high dielectric strength, and machinability. Most resins also meet FDA requirements and colors can be molded in.
It would appear that rotational casting techniques would be ideally suited for the production of large capacity pump casings. However, the inherent capability of producing a uniform wall thickness by rotationally casting a pump casing results in flange connections which are too thin to perform their intended purpose. Moreover, relatively thin flange sections tend to move or warp when pressure is applied. It is desirable, therefore, to produce a rotationally molded pump casing having thickened casing flanges which are reinforced to maximize connecting strength and minimize warpage under pressure.